Loud horn noise after unvented cylinder service

[Sard]

Hi all,

I've just had my unvented cylinder serviced and the expansion vessel repressurised (it had lost pressure completely) and I was getting a drip through the tundish. Now the cylinder/expansion vessel makes a really loud and unbearable noise (like a fog horn) everytime we turn the taps on.

Any ideas on what's causing this? I have contacted the plumber who did the service but wanted to get some advice on here too.

 

[Madrab]

It is usually down to the EV pre-charge pressure not being correct, does it stop after a bit when running the HW? Can aslo be an issue with the Pressure Reducing Valve, depends where it is vibrating

 

[Sard]

Sorry for the late reply, the noise stops after a while when the hot water is running. I'd say after 5-10 seconds. Shall I let some air out? Also the EV was taken off and the water was pumped out using a bike pump before it was repressurised if that helps?

 

[Johntheo5]

When the EV was removed and if it had been installed "upside" down with water end on top then the water should have just run out when inverted?.
The pre charge pressure should have been set (pumped) to the PRV pressure - 0.2bar, the PRV is normally set to 3bar so the precharge pressure should be 2.8bar.

 

[TR888]

Hi Sard
Did you get to the bottom of this?
Were in the same position - new EV, loud foghorn noise for 5-10 secs when hot water tap turned on.
Thanks

 

[DP]

Sorry for the late reply, the noise stops after a while when the hot water is running. I'd say after 5-10 seconds. Shall I let some air out? Also the EV was taken off and the water was pumped out using a bike pump before it was repressurised if that helps?

Easier to do it that way unless you have a proper air pump, Which any good engineer will have. Never had to remove the vessel to pressurise. If new vessel being fitted, pressure before fitting

 

[Johntheo5]

Hi Sard
Did you get to the bottom of this?
Were in the same position - new EV, loud foghorn noise for 5-10 secs when hot water tap turned on, plumber ghosting me.
Thanks

Was the new EV installed because of the foghorn noise occuring with the old EV as well?
What make/model of UV cylinder? and what are the UV cylinder and EV volumes?.

 

[TR888]

Hi

No it was changed because we had dripping through the tundish - we’ve had the prv, combination valve and EV changed as the plumber wasn’t sure what was causing it.

It’s a Range Tribune HE cylinder, I’ve attached the specs if that’s what you mean by volumes? Sorry, I’m a bit green on this! Not looking to attempt a diy job, just £500 in with a plumber and still have issues so want to understand for when I get the next one in.

 

[Madrab]

Most of the time, there isn't an issue with just fitting the Expansion Vessel (EV) as it is. The problem can occur when there's a mismatch in pressures between the mains and pressure in the EV when the cylinders full and full heated and the EV can resonate, either that or it's the Pressure reducing valve on the control group vibrating.

Does this usually happen when the unvented hasn't been used for a while, say overnight.? Do you know if the EV is connected to the HW pipe coming out of the top of the cylinder or not?

The system needs a bit of fine tuning and your engineer should be happy to do that.

 

[Johntheo5]

Hi

No it was changed because we had dripping through the tundish - we’ve had the prv, combination valve and EV changed as the plumber wasn’t sure what was causing it.

It’s a Range Tribune HE cylinder, I’ve attached the specs if that’s what you mean by volumes? Sorry, I’m a bit green on this! Not looking to attempt a diy job, just £500 in with a plumber and still have issues so want to understand for when I get the next one in.

I probably should have said capacity, you have a 150L cylinder and a 12L EV which should be fine, if the whole cylinder is heated to 65C then there will be slightly less than 3L (2.75L) of expanded water in the EV at a pressure of 4.2bar which should again be fine, assuming the EV was properly precharged to 3.0bar., the noise you are getting fot this ~ 10sec is probably this 2.75L of water coming from the EV through the tap in falling from 4.2bar to 3.0bar. Seems strange to have changed the PRV, combination valve and the EV so you don't really know whats going on. You wouldn't be breaking any rules IMO if you have a tyre pressure gauge and just take the pressure at the schrader valve on the EV air end with no HW draw off and with that same tap opened, it might show up something.

 

[TR888]

Thanks for the replies.
Yes this usually happens when it has been left a while, such as overnight.
Not sure if hot water pipe is connected to EV, attached a pic for reference.
So in conclusion the pressure likely needs adjusting on the EV? I’m guessing this isn’t dangerous at the moment until I can get someone in?

 

[Madrab]

Yes - safe enough.
As suggested it's usually the mismatch in pressures between the mains and the output pressure from the EV at that initial release of water from the EV when the cylinder is full and is fully heated, it stops once that pressure balances. Would it be fair to say you get a little rush in pressure too then it settles down?

Mention the symptoms to the engineer you call in so he is aware of what the problem is. Ask him if he has seen it before and has corrected it. That'll show he has the experience to sort it out. Too many times I've heard of people coming across this issue and it takes multiple 'pros' to visit till they finally get someone who has the experience to sort it out for them. Another thing I notice is some 'Pro's don't fit gauges to the control group when fitting, makes life so much easier when setting up, though that one would be easy to temp fit one due to where the loop is fitted.

 

[TR888]

So the saga continues.

Original plumber has been back out and the pressure in the EV has been adjusted a couple of times and we’re now at 2.6bar. Still got the issue.

After more investigating from me, it seems that it only makes this noise when the hot water tap for the bath is turned on after the water has been heated. I’ve tried other basin taps and downstairs taps and it doesn’t happen. It is a mixer tap but one with separate handles for hot and cold - the only one like it in the house, all of the others are single mixers.

Is this possibly as simple as needing a new tap? Surely not a coincidence that we’ve had all this work done and then the taps gone?

I’m not sure if it is relevant but, as part of fixing the dripping tundish issue, I mentioned to the plumber that the shower in the same bathroom drips from the actual fitting when the hot water is warming up in the tank. It didn’t do this any other time, only when the hot water was on. We had a new shower fitted so it doesn’t do this anymore.

Again, not sure if this is relevant but we’re in a 2 storey house and the pressure for the tap basin on the top floor en suite has dropped noticeably since this issue started.

Appreciate any insight before I give up and sell the house

 

[HERTS P&D]

Faulty tap.

Andy